Feasibility of next generation non-linear beamforming ultrasound methods to characterize and size kidney stones
Advanced ultrasound beamforming methods for imaging kidney stones may help address the sensitivity and size overestimation problems with standard B-mode ultrasound. The study objective was to demonstrate feasibility of advanced ultrasound beamforming methods including plane wave synthetic focusing (PWSF), short-lag spatial coherence (SLSC) imaging, mid-lag spatial coherence (MLSC) imaging with incoherent compounding, and aperture domain model image reconstruction (ADMIRE).
The ultrasound techniques were evaluated using a research-based ultrasound system applied to an in vitro kidney stone model (n=12, 4 and 8cm depths) and in a pilot study of human stone formers (n=5). Stone diameter sizing, shadow contrast, and stone contrast were compared among the different techniques and to B-mode. CT measurements were used to determine true stone size in the pilot study. Analysis of variance was used to analyze the differences among group means, and t-test when comparing to B-mode, with p<0.05 considered significant.</p>
All stones were detectable with each method. In the in vitro study, MLSC performed best compared to B-mode for mean stone contrast (31.7 dB vs 14.7 dB, p<0.0025). On average, B-mode sizing error ± SD was >1mm (1.2±1.1 mm), while those for PWSF, ADMIRE, and MLSC were <1mm (-0.3±2.9mm, 0.6±0.8, 0.8±0.8, respectively). The mean posterior stone shadow contrast was highest with ADMIRE overall (p<sub>trend=0.008), and when comparing between ADMIRE and B-mode (8.0 dB vs 2.1 dB, respectively; p=0.0131). In the pilot clinical study (Figure), mean stone contrast was best with ADMIRE and MLSC than with B mode (28.5 dB and 27.8 dB vs 18.1dB, respectively; ptrend=0.002). Mean sizing error was best with ADMIRE (+1.2mm), however there was no statistically significant difference when compared with B mode (+2.7mm).
The detection and sizing of stones are feasible with advanced beamforming methods with ultrasound. ADMIRE and MLSC hold promise for improving stone contrast, shadow contrast, and reducing sizing error. Future work will include imaging a broader population of human stone formers.
Funding: Vanderbilt Institute of Surgery and Engineering (VISE) Pilot and Feasibility Award, VISE Surgeon in Residence Award, R01EB020040.